While considerable attention has been given to mapping sites of solar radiation-induced mutations in a number of skin cancer-related genes, less is known about the overall distribution of the original DNA damage and how that damage influences replication and genomic integrity. The goal of this revised R21 project is to initially visualize and analyze the distribution of specific photoproducts (e.g. cyclobutane pyrimidine dimers (CPDs) and [6-4] pyrimidine-pyrimidone photoproducts (6-4PPs)) and relate sites of damage to selected genomic locations and areas undergoing replication. We will then determine whether specific chromosomal regions or genes associated with different types of skin cancer, such as p53 (basal cell carcinomas and squamous cell carcinomas), PTCH1 (basal cell carcinomas), CDKN2A (melanoma), chromosomal region 9p (basal cell carcinomas), are more susceptible to UV-induced DNA damage formation or replication stalling. These two factors increase risk for point mutations through error-prone translesion synthesis and for deletions and translocations originated during the recombinational repair of the stalled replication forks that have collapsed. PUBLIC HEALTH RELEVANCE: While considerable attention has been given to mapping sites of solar radiation-induced mutations in a number of skin cancer-related genes, less is known about the overall distribution of the original DNA damage and how that damage influences replication and the probability of mutation fixation. The goal of this R21 project is to initially visualize and analyze the distribution of specific photoproducts and relate the damage sites to selected genomic locations and areas undergoing replication. We will then determine whether genes associated with skin cancer formation are more susceptible to UV- induced DNA damage formation or replication stalling. These two factors increase risk for point mutations through error-prone translesion synthesis and for deletions and translocations originated during the repair of double-strand DNA breaks that are formed by the collapse of replication forks.